In a conventional GSM (Global System for Mobile Communication) network, a wireless services subscriber has a wireless MS (Mobile Station) which is assigned an IMSI (International Mobile Subscriber Identity). The IMSI is uniquely associated with the subscriber, and is stored in a Subscriber Identity Module that is installed in the wireless telephone.
The subscriber's PLMN (Public Land Mobile Network) maintains a subscription with the local subscriber for the provision of local telecommunications services. As part of that subscription, the home PLMN maintains a static association between the local subscriber's and a local MSISDN (Mobile Subscriber ISDN Number) directory number that is uniquely associated with the subscriber.
The PLMN includes a Home Location Register HLR (Home Location Register), and one or more MSC/VLRs (Mobile Switching Centre/Visitor Location Register). Any one of the MSC/VLRs will be in communication with the subscriber's MS as the subscriber roams within the PLMN. The MSC/VLR currently in communication with the MS maintains the subscriber's IMSI and MSISDN directory number, and a IMSI (Temporary Mobile Subscriber Identity). The IMSI is a temporary identifier that is local to the servicing MSC/VLR and used by the MSC/VLR. to temporarily identify the MS.
The HLR maintains Subscriber Data associated with the subscriber, including the subscriber's IMSI, associated MSISDN directory number, and the MSC/VLR that is currently servicing the MS.
An originating party originates a telephone call with the subscriber by dialing the subscriber's MSISDN directory number from the party's PSTN (Public Switched Telephone Network). The PSTN forwards the MSISDN directory number to a GMSC (Gateway Mobile Switching Centre) that is associated with the subscriber's PLMN. The GMSC, in turn, forwards the MSISDN directory number to the subscriber's HLR, and requests that the HLR provide routing information which the GMSC can use to terminate the telephone call.
Using the MSISDN directory number, the HLR. identifies the servicing MSC/VLR, and requests that the MSC/VLR provide the requested routing information. The MSC/VLR replies with a temporary MSRN (Mobile Station Roaming Number), and maintains an association between the MSRN and the subscriber's IMSI.
The GMSC uses the MSRN to route the telephone call to the servicing MSC/VLR. The servicing MSC/VLR terminates the telephone call at the MS using the IMSI associated with the MSRN, and then makes the MSRN available for use in subsequent terminating calls.
A problem with the conventional GSM network is that the MSISDN number is local to the subscriber's home PLMN. Therefore, if a subscriber roams outside the subscriber's home PLMN, in order to provide the subscriber with telecommunications services within the visited PLMN the visited PLMN must first contact the subscriber's home PLMN to obtain the subscriber's Subscriber Data. If the Subscriber Data reveals that the subscriber is entitled to telecommunications services within the visited PLMN, the subscriber can then originate a call within the visited PLMN. Thereafter, if a call is issued to the subscriber's home MSISDN number while the subscriber's mobile terminal is in the visited PLMN, to terminate the call the home PLMN must forward the call to the visited PLMN which, in turn, terminates the call to the mobile terminal, as described above.
To offset the costs of this additional overhead, typically a subscriber must pay roaming charges if the subscriber roams outside the subscriber's home PLMN and receives a terminating call to its home MSISDN number. These charges are payable even if the party that originated the call and the subscriber are both resident within the same visited PLMN.
Similarly, if the subscriber originates a telephone call outside the subscriber's home PLMN, the subscriber must pay roaming charges even if the subscriber and the party that received the call are both resident within the same visited PLMN. As a result, attempts have been made to reduce the applicability of roaming charges as a wireless subscriber roams between PLMNs,
One solution has been to negotiate roaming agreements between PLMNs. These agreements typically limit the roaming charges that would be payable as wireless subscriber roams between PLMNs.
Bijanki (U.S. Pat. No. 6,539,223) teaches a mobile telecommunications system that includes a HLR having entries associating the identity (e.g. IMSI) of a mobile telecommunications device with a plurality of MSISDN directory numbers. In the process of terminating a telephone call from a MSC, the HLR uses supplemental information, such as the geographical location of the mobile telecommunications device, to determine which of the directory numbers to use for the purpose of telephone call termination, The supplemental information may be provided to the HLR either from the MSC, or a GPS unit associated with the mobile telecommunications device.
Typically, the HLR includes a home MSISDN directory number (MN) associated with the mobile's home sector, and a mobile MSISDN directory number (MDN) associated with a sector other than the mobile's home sector. If the mobile telecommunications device is located within its home sector, and a call to the HDN originates from a PSTN, the MSC terminates the call to the mobile via the HDN. However, if the mobile telecommunications device is not located within its home sector, the MSC does not terminate the call to the mobile. Instead, if the user of the mobile has activated a call-forwarding feature to the mobile's MDN, the MSC forwards the call to mobile via the MDN.
Thakker (U.S. Pat. No. 6,907,242) teaches a method and system for providing local telecommunications services to visited subscribers of a GSM network. According to the method, a home PLMN transmits a non-local subscriber's IMSI to a local PLMN, requesting that the local PLMN provide telecommunications services for the non-local subscriber. In response, the local PLMN creates a local subscription for the non-local subscriber, which includes, at a minimum, a local MSISDN directory number that is uniquely associated with the subscriber. Thereafter, the local PLMN maintains a mapping between the non-local subscriber's IMSI and the unique local MSISDN directory number.
When the non-local subscriber's visits the local PLMN, the local MSC/VLR initiates a location update with the subscriber's Home Location Register HLR (Home Location Register) and receives, in response, the non-local subscriber's Subscriber Data. The local MSC/VLR updates the local HLR with the subscriber's new location, using the unique local MSISDN directory number associated with the non-local subscriber's IMSI The local HLR then responds to the local MSC/VLR. with an ISD (Insert Subscriber Data) message.
Thereafter, local calls to the non-local subscriber's unique local MSISDN directory number are directed to the non-local subscriber via the local HLR. After a predetermined period of time, or the usage of a predetermined number of air-time minutes, the local HLR purges the mapping between the unique local MSISDN directory number and the non-local subscriber's IMSI, and returns the unique local MSISDN directory number to a pool in the local PLMN for subsequent remapping.